1. Field of the Invention
The present invention relates to a reception apparatus and reception method, more particularly, a diversity system reception apparatus and reception method which obtain excellent reception conditions using a selected antenna set.
2. Description of the Related Art
FIG. 1 illustrates the whole configuration of a conventional diversity system reception apparatus. The reception apparatus is composed of 8 reception antennas 1 to 8, reception RF sections 9 to 16 of which the number is the same as that of reception antennas, signal combining section 17, and demodulation section 18.
In the reception apparatus with the above-mentioned configuration, received signals received at reception antennas 1 to 8 are inputted to reception RF sections 9 to 16 to output downconverted signals with an intermediate frequency, respectively. The intermediate-frequency signals are subjected to equal-gain combining or maximal-ratio combining in signal combining section 17, and then demodulated in demodulation section 18. The demodulated message is thus finally obtained.
However, in the reception apparatus, since it is necessary to prepare reception RF sections 9 to 16 of which the number is the same as that of reception antennas 1 to 8, there is the problem that the circuit scale for signal processing becomes large. Further, since complicated signal processing such as subjecting each received signal to weighting to combine, in order to obtain diversity effects as much as possible, there is another problem that it takes a relatively long time to process signals.
In order to solve such problems, proposed is a diversity system reception apparatus disclosed in Japanese Unexamined Patent Publication HEI9-307492.
FIG. 2 illustrates a configuration of the above-mentioned reception apparatus. Antennas 21 to 24 each has a radiation pattern, and receives a radio signal with the radiation pattern. Selection section 25 receives a control signal from control section 26 and transmits a received signal for each antenna to comparison section 27 sequentially, while having the function for selecting an antenna for use in reception. Comparison section 27 compares a level of the received signal, and transmits the compared result to control section 26. Based on the compared result, control section 26 transmits the control signal instructing to select an antenna with the largest received level and another antenna with the second largest received level.
Combining section 28 subjects received signals from antennas that selection section 25 selects to phase control and amplitude control, and then combines the resultant signals. Reception section 29 receives a combined received signal to output a desired signal.
Operations in the reception apparatus are next explained. First, received signals received at antennas 21 to 24 are transmitted sequentially to comparison section 27 through selection section 25. Comparison section 27 compares a level of the received signal from each of antennas 21 to 24 to each other, and transmits the compared result to control section 26. Based on the compared result, control section 25 controls selection section 25 to select an antenna with the largest received level and another antenna with the second largest received level. Thus, the received signals from selected antennas are only combined in the combining section after being subjected to the phase control and amplitude control, and then transmitted to the reception section. The optimal reception conditions are thus achieved.
As described above, according to the reception apparatus, since received signals only from two antennas selected from among antennas 21 to 24 are signal-processed, the circuit scale for the signal processing can be reduced.
However, in the reception apparatus disclosed in Japanese Unexamined Patent Publication HEI9-307492, since an antenna is selected based on a received quality obtained with the antenna alone, the combination of antennas which provides the best received quality of a combined signal is not always obtained. Further, in the case where the antenna is selected based on the received quality of the combined signal, since the number of combinations of antennas of which the received quality is compared increases exponentially as the number of antennas is increased to improve the diversity effects, the antenna selection method becomes complicated.
When the antenna selection method thus becomes complicated, since the complicated comparison method and control are necessary, the circuit scale becomes large, causing the problem that it takes a longer time to select antennas. As a result, the conventional problem is not solved.
An object of the present invention is to provide a reception apparatus and reception method that achieve excellent reception conditions in a short time with a small-scaled calculation circuit using a simple selection method.
The present invention provides the reception apparatus that handles as a unit an antenna set with antennas combined in advance. Specifically, in selecting antennas for use in reception, handling the antenna set as the unit, the reception apparatus collectively selects antennas using as a criterion qualities of received signals received at the antenna set.
Since the apparatus thus handles the antenna set as the unit, it is possible to limit the number of calculation times for received qualities to be needed as the criterion for the antenna selection and the number of combinations of target antennas for the antenna selection, as compared to the case where each antenna is handled as the unit. Accordingly, it is possible to achieve excellent reception conditions in a short time with the small-scaled calculation circuit.
Further, the antenna set according to the present invention is composed of antennas which are selected in advance from among some antenna groups so that the antennas belonging to the antenna set forms a predetermined radiation pattern.
Since the antennas belonging to the antenna set thus form the predetermined radiation pattern, it is possible to achieve the excellent reception conditions assuredly even though a simple selection method handling the antenna set as the unit is used.